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Open Roads Forum  >  Tech Issues

 > Trimetric vs Peukert Question-ANSWER?

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MEXICOWANDERER

las peƱas, michoacan, mexico

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Posted: 07/01/12 01:29pm Link  |  Print  |  Notify Moderator

Not a contest Wizzie.
My opinion is that yes, it has to be a fundamental electrochemical exercise and treated as such. How does one conceptualize chemical reactions by leaving them out of the workup? Beats me. Like balancing a checkbook without knowing where zero is.

Trying 50% cycling of a VRB for 90 days using an amp hour meter and then see where you are. It isn't a slam dunk unless you have a lot of splurge charging capability. Then determine how much capacity you have or have not lost. You have to do it by testing and then rely on instrumentation trends and tendencies.

MrWizard

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Posted: 07/01/12 02:18pm Link  |  Print  |  Notify Moderator

MEXI

i just meant, your vast knowledge might have a different take on what i was saying, and i'm not even thinking of VRB/AGM

i just meant about my speculation about chemical reaction sustaining c5 until 50% or less then taking a drop in capability as reaction slows


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ktmrfs

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Posted: 07/01/12 09:39pm Link  |  Print  |  Notify Moderator

Matt_Colie wrote:

BFL,

Peukert exponent is specific to each individual battery design. Trimetric does not know about that, but it can guess and be pretty close but only if that unit is programmed correctly.

You need to start working with specific gravity and temperatures to get real numbers that will be correct for your batteries.

If you look at you table, you will see that their US125 takes less of a beating during a hard-short drain than does US2200. This is what Trimetric has to be programmed to understand.

Did anybody bother to tell you that taking any lead/acid battery below a 50% charge will necessarily cause a permanent loss of capacity?

Matt


trojan reps claim that on the golf carts you can run them down to 20-30% of capacity for hundreds of cycles w/o reducing capacity noticeably. It will decrease the cycle life.

but they also said don't try that on the trojan 12V deep discharge, anything below 50% does quickly decrease capacity.

I believe trojan since I have a pair of GC that are discharged to 30% sometimes 20% of capacity about 30 times year and are 8 years old still showing close to the original 240A capacity. Thats over 240charge discharge cycles to 30% of capacity or so.


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mena661

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Posted: 07/01/12 11:16pm Link  |  Print  |  Notify Moderator

ktmrfs wrote:


I believe trojan since I have a pair of GC that are discharged to 30% sometimes 20% of capacity about 30 times year and are 8 years old still showing close to the original 240A capacity. Thats over 240charge discharge cycles to 30% of capacity or so.
That's great info! Good to see that they work as advertised.


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BFL13

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Posted: 07/03/12 11:55am Link  |  Print  |  Notify Moderator

Thanks for the ideas. I have found in past tests that SG does falls off faster when nearing 50% rather than staying linear like some graphs show it doing on discharge. I do need to try this again when I can be more accurate, which may take out some of the discrepancy.

My main thought is that it must have something to do with the recovery after you stop the discharge. IE, if I left the 90amps on all the way till the batteries went flat, then it would show the "correct" capacity for Peukert.

But stopping and then waiting for voltage to bounce back lets the battery recover somewhat. It is known that you can stop a high discharge, wait a bit, and then get more from the battery at a low discharge. That doesn't really explain this question, but it could be something to do with it.

I won't be able to run trails till after this camping season, so it will be a good while.


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BFL13

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Posted: 07/03/12 12:03pm Link  |  Print  |  Notify Moderator

MrWizard wrote:

Quote:

Here is a Peukert for the US2200 and US 125 which are most like my 6s, where a pair of each would match my bank for AH at 460ah


i think you mean (2) pairs, (4) 6's

as one pair is only 230 AH at 12v


I think "a pair of each" means two pairs. I have a pair of Exide GC135s at 226ah (similar in ah to the table's 225 for the 2200 and a pair of Interstate GC2 XHDs at 232 (similar to the 125's) so my total rated is 458 vs the 460 The battery chemistry is not the same so this could throw things off a little.

KendallP

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Posted: 07/03/12 01:21pm Link  |  Print  |  Notify Moderator

I almost feel silly asking ol' BFL-"Tinkering in the shop is never time wasted"-13 this question but...

have you run the same test on the same bank at the 20hr rate yet?

Perhaps you have more than rated capacity.


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pianotuna

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Posted: 07/03/12 01:48pm Link  |  Print  |  Notify Moderator

Hi BFL13,

I think (correct me if I'm wrong) an inverter load was used for testing in the past--that would skew the results as the 12 volt voltage drops off.


Regards, Don
Full Time in a Kustom Koach Class C 28'5", 256 watts Unisolar, 875 amp hours in two battery banks 12 volt batteries, Magnum 3000 watt PSW inverter.

wa8yxm

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Posted: 07/03/12 02:06pm Link  |  Print  |  Notify Moderator

Just one question: Are the batteries BRAND NEW?

Often a brand new battery needs a few cycles to come up to full capacity... and once it hits full capacity it then starts to "Age" and by that I mean LOOSE capacity.

So the 230 amp hour per six volt pair, is The PEAK capacity,

Oh, by the way. By now I would suspect that your testing would have them "Broke IN" properly. (That is up to full capacity) if they were new when you started.

Also note this "Break in" period is what a company rep told another forum member. I have not, personally, made any attempt to prove it.

Also note that the temperature affects capacity on batteries, and it has been HOT OUT lately.


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mena661

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Posted: 07/03/12 03:36pm Link  |  Print  |  Notify Moderator

wa8yxm wrote:

Also note this "Break in" period is what a company rep told another forum member. I have not, personally, made any attempt to prove it.
Mine took about 8 months to "break in". I think I have a thread about it somewhere here. I think BFL's were broken in a week after he bought them.

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